Many large motorized vehicles have a clutch assembly to selectively connect an engine of the vehicle with the vehicle transmission. The workings of such a clutch assembly can be discovered by a review of U.S. patent application Ser. No. 12/807,971, Franke, entitled Dry Clutch Having Solid Lubricant Friction Stabilization Inserts, filed Sep. 17, 2010 (the disclosure of which is incorporated by reference herein). Referring to FIGS. 1, 7 and 11, a conventional driven disc assembly 9 includes a disc member 11. The disc member 11 is torsionally connected with a damper unit 13 which spring dampens torsional vibrations delivered to an input shaft of a transmission. The disc member 11 is typically a thin metallic plate having along it's periphery a series of blades or wings 15. The wings 15 on opposing faces have connected thereto a friction pad 17. The friction pad 17 consists of a backing plate 19 with a connected friction material, commonly a ceramic friction material 21. The friction material 21 is referred to as the button in many applications. The friction pads 17 are connected to the friction disc 11 by a series of flathead semi-tubular rivets 23. Referring the addition to FIG. 11, the flathead semi-tubular rivets 23 have a purchased head 25 and a peened head 27 formed by an assembly operation.
The overall axial width 29 (adjacent its outer diameter) of the driven disc assembly 9 based upon the design of the driven disc assembly 9 and a clutch intermediate plate and/or clutch cover assembly that the driven disc assembly interacts with. The overall axial width (sometimes also referred to as height) of the buttons 21 is determined by two factors. The first factor is the expected wear life of the button and is determined by a dimension 31. The second dimension is a dimension 33 that is a width of the friction material on the backing plate required for clearance of the rivet head 27 (or on the other side 25). Accordingly, the amount of friction material of a width 33 is essentially wasted material that cannot be utilized. Typically, the ceramic material making up the button is a very expensive material that typically far exceeds the cost of the backing plate 19. The backing plate is typically a metallic material.
One attempt to eliminate or to make more use wasted button material is provided in FIGS. 6 and 10. In FIGS. 6 and 10, a recessed rivet driven disc assembly 41 is provided. In the driven disc assembly 41, the backing plates 43 have adjacent to the rivet holes recesses 45. Because of the recesses 45, a specialty axially shortened rivet 47 is utilized. The driven disc assembly 41 in FIGS. 6 and 10 does provide an advantage of shortening the rivet, allowing a greater portion of the buttons 48 to be utilized. However, since the overall thickness 29 of the driven disc assembly is determined by other design criteria, the recessed design of driven disc assembly 41 mandates even thicker buttons 48 (to achieve an overall axial thickness 29) thereby providing a button with more excess material which cannot be utilized (due to clutch design) and thereby increasing driven disc assembly cost.
Referring to FIGS. 2 through 5 and 9, an alternative design driven disc assembly 61 has been put forth. Driven disc assembly 61 has an overall axial width 29. In driven disc assembly 61, the disc 11 can be utilized. Driven disc assembly 61 has a backing plate 63 that has an elevated flat section 67 that is elevated by a series of dimple mounds 69. The dimple mounds 69 raise an outer surface of the backing plate 63 outward so that the button 71 can have an effective thickness 31 thereby eliminating the non-utilized thickness 33 of the button in the conventional used driven disc assembly 9. Although this design did provide the advantages desired in reduction of friction material utilized, the non-flat contact between the section 67 of the backing plate with the disc caused the backing plate 63 to buckle due to the lack of adequate heat transfer from the backing plate 63 to the disc 11.
It is desirable to provide a driven disc assembly wherein the thickness of the friction button can be reduced to its effective use to minimize the costs of the driven disc assembly without compromising operational performance.